1. Field of the Invention
The present invention relates to a system and method for processing multimedia packets and, in particular, to a system and method for processing multimedia packets for access in real time or near real time.
2. Background of the Related Art
The ordinary function of a Media Access Control (MAC) layer of a local area network (LAN) is to enable many stations to access common channels with minimum interference and with a high performance rate. Generally, the Carrier Sense Multiple Access (CSMA)/Collision Avoidance (CA) method is used. This is a contention-based method of the asynchronous traffic, in which all stations have equal rights to access the network. In this method, Request To Send (RTS) and Clear To Send (CTS) confirmation functions are added to the collision avoidance function for securing stability in packet transmission.
The related art MAC processor of a wireless LAN conducts exponential random back-off process using the CSMA/CA method for data transmission. The exponential random back-off processes are conducted whenever the medium, to which a station tries to transmit a MAC Protocol Data Unit (MPDU), is detected as busy. The back-off process is selected by an equation of the random back-off time. The back-off timer decrements by slot times in which the medium has been free. While the medium is busy, the back-off timer stops. The back-off timer restarts to decrement when the period in which the medium has been free is determined to be longer than the Distributed Inter-Frame Space (DIFS). The data transmission commences whenever the back-off timer reaches zero.
After an MPDU is transmitted, stations having other MPDU conduct the above-described back-off process. Here, it is necessary to ensure that stations have fair and equal chances to access the medium. While multiple stations are waiting and the random back-off process is conducted, the station that selected the shortest waiting time through the random function wins in the access contention.
The above-described method has strength in that fair access is ensured based upon the first-come, first-served, principle because the station which lost in a contention has a shorter back-off delay period after the next DIFS than other stations which participated in the back-off for the first time.
FIG. 1 is a diagram illustrating the back-off process of a MAC processor in a related art wireless LAN. As shown therein, the back-off process is conducted in order to enable a station that is waiting comparatively for a long time to have an increased chance for accessing the channel. The waiting time for a station that has lost in a prior contention is decreased. When the RTS/CTS message exchange is conducted, a collision occurs only if two or more stations select a same time slot. Then, these stations reenter the contention status with contention window values, which increase in number exponentially.
For example, if a station wants to send data, but the channel is already occupied, the station must wait until the prior use finishes. After a DIFS time elapses, a time slot within the back-off window is randomly selected.
Then, a station that selected the initial time slot starts transmission. Only if two or more stations selected the same time slot will a collision occur. A station that lost in the contention because another station selected the initial time slot freezes the back-off counter. In the immediately following contention, the station that has lost in the previous contention is provided with a high priority as it waits for the remaining time slot.
The related art system and method for processing multimedia packets have various disadvantages. For example, where audio or video are transmitted, the data transmission is often suspended due to the delayed access. Also, in the related art random back-off method, randomly determining the transmission priority based upon the transmission rate may significantly affect the throughput. Therefore, in the related art wireless LAN, it has been virtually impossible to process audio or video data in real time due to such problems.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.